board: gateworks: venice: add imx8mp-gw71xx-2x support

board: gateworks: venice: add imx8mp-gw71xx-2x support

The Gateworks imx8mp-venice-gw71xx-2x consists of a SOM + baseboard.

The GW702x SOM contains the following:
 - i.MX8M Plus SoC
 - LPDDR4 memory
 - eMMC Boot device
 - Gateworks System Controller (GSC) with integrated EEPROM, button
   controller, and ADC's
 - PMIC
 - SOM connector providing:
  - eQoS GbE MII
  - 1x SPI
  - 2x I2C
  - 4x UART
  - 2x USB 3.0
  - 1x PCI
  - 1x SDIO (4-bit 3.3V)
  - 1x SDIO (4-bit 3.3V/1.8V)
  - GPIO

The GW71xx Baseboard contains the following:
 - 1x RJ45 GbE (eQoS from SOM)
 - off-board I/O connector with I2C, SPI, UART, and GPIO
 - Front Panel bi-color LED
 - re-chargeable battery (for RTC)
 - PCIe clock generator
 - 1x USB Type-C connector supporting USB 2.0 host mode with VBUS
 - 1x MiniPCIe socket with SIM, PCI/USB 3.0 (mux), and USB 2.0
 - GPS
 - Accelerometer
 - EERPOM
 - Wide range DC input supply

Signed-off-by: Tim Harvey <tharvey@gateworks.com>